1. Field of the Invention
The invention relates to the production of pourable powdered rubber. More specifically, the invention relates to a process for preparing pourable powdered rubber by mixing a rubber latex with a filler suspension containing a precipitant.
2. Discussion of the Background
The rubber industry has been increasingly concerned and interested in powdered rubbers and processes for producing the same. Present rubber technology uses primarily raw rubber material which is in the form of bales. Current rubber processing technology utilizing bale rubber requires a high cost in time, energy and personnel.
The mastication of the bale, and the intimate mixing with fillers, mineral oil plasticizers, and vulcanization accelerators are carried out on rolls or in kneaders. To avoid reductions in quality, the mixtures are prepared in several steps and the mixture is generally stored between steps. Extruder-pelletizers or extruder-roller dies generally follow the kneaders or rolls.
Only a completely new processing technology can lead the way out of this extremely unsatisfactory and costly technique of rubber processing. The use of pourable powdered rubber has been discussed and tested in recent years, because it provides the possibility for processing rubber mixtures simply and rapidly, like thermoplastic powders.
Several methods for producing powdered, pourable rubber-filler mixtures, especially rubber-carbon black mixtures based on general purpose rubbers, have already been found and described (see DE-PS 21 35 266 and PS 24 39 237; DE-AS 22 14 121; DE-OS 22 14 121; OS 23 25 550, OS 23 32 796, and OS 26 54 358). Important features of the processes described in these references are the use of special surface-active compounds and a costly, multistep precipitation technique.
Since the main objective of using powdered rubbers is to decrease costs in the area of rubber processing, a basic prerequisite for the success of these efforts is the economical production of rubbers in powdered form.
A process for producing powdered rubber is described and claimed in DE-PS 28 22 148. An important drawback to this process is the fact that not only are powders produced with particles of various sizes, but that they have a relatively high content of filler with decreasing particle size. This can result in problems during processing in the form of particle segregations. Segregation of particles results in variable filler contents in the molded parts prepared from the powdered rubbers.